The US air safety regulator has confirmed that its directive for airlines to fix cracking and corrosion on the fuselage of Boeing 777 planes applied to MH370, the Malaysia Airlines jet that disappeared en route to Beijing over the weekend.

But Boeing insists the plane was not covered by the directive, nor any related service bulletins.The Federal Aviation Administration issued a worldwide alert last year after discovering a 40-centimetre crack on one plane, underneath the plane’s satellite antenna and warning that the flaw ''could lead to rapid decompression and loss of structural integrity of the airplane''.

A woman writes a message of support for the passengers of the missing plane on a banner at Kuala Lumpur airport. Photo: Reuters

The airworthiness directive, which was finalised on February 18 this year but not published until March 6, listed the models of Boeing 777 aircraft affected by the directive but didn’t explicitly mention the Boeing 777-200ER model, the variant that was MH370.

However, a spokesman for the FAA, Allen Kenitzer, told Fairfax Media that MH370 was covered by the directive.

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''The FAA does not recognise the 777-200ER as a separate model, since it is not listed on the Type Certificate Data Sheet (TCDS). Any Airworthiness Directive (AD) that includes the 777-200 will also include the '-200ER,' unless the effectivity is limited by airplane line number or some other factor.’’

Asked directly if the MH370 was covered by the directive, Mr Kenitzer replied in an email: ‘‘Yes’’.

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However, Boeing released a statement saying the type of antenna in question was not installed on MH370.

Malaysia Airlines chief executive Ahmad Jauhari Yahya told reporters on Wednesday: ''We ensure that all our aircraft are airworthy and comply to all the ADs and the SBs [service bulletins].''

But asked whether the missing Boeing 777-200ER had been checked for the specific problem following the FAA directive, he admitted he would have to ''check on the record'' whether tests had taken place yet.

''Generally, every aircraft … has to comply,'' he told London's Telegraph. ''But you must understand that certain directives have a timeline to be complied [with].''

A spokesman for Malaysia Airlines had confirmed on Tuesday that the missing aircraft had been serviced on February 23, with further maintenance scheduled for June 19.

The FAA first uncovered the flaw in June last year, publishing its concerns in September and updating the information in November. But its final directive wasn’t finalised until February 18, and was made public on March 6. MH370 went missing at about 1.30am on March 8.

Any structural failure related to the flaw could not only have led to a decompression that left the 239 passengers and crew on the missing flight unconscious, it would also have disabled satellite communications, including the Aircraft Communications Addressing and Reporting System (ACARS), which transmits data of the plane’s location automatically.

It would also have rendered the plane invisible to all but ''primary radar'', which has a range of only 100 nautical miles. If any rupture of the fuselage was not catastrophic and led to the plane disintegrating, the plane could have continued on autopilot for up to seven hours, taking it well away from its last confirmed position – and possibly beyond the search area – before running out of fuel.

Such an incident took place with a Helios Airways flight in 2005, where 121 passengers and crew died.

And, in 1999, a Learjet carrying golfer Payne Stewart crashed into a field in the US state of South Dakota after flying uncontrolled for several hours after those on board apparently became unconscious due to a lack of oxygen brought on by a loss of cabin pressure.

According to a post on the Professional Pilots Rumour Network, the end of satellite communications may not have disabled the mobile phone network on the plane, which runs off a different communications system.

Nineteen families signed a statement saying they were able to telephone the mobile phones on the plane. While they got a dial tone, no one picked up.

‘‘A slow decompression [e.g. from a golf ball-sized hole] would have gradually impaired and confused the pilots before cabin altitude [pressure] warnings sounded,’’ the post said. ‘‘If the decompression was slow enough, it’s possible the pilots did not realise to put on oxygen masks until it was too late. [It] also explains why another pilot 30 minutes ahead heard ‘mumbling’ from MH370 pilots. [VHF comms would be unaffected by SATCOM equipment failure].’’

Any lack of oxygen caused by the rupture would eventually kill passengers and crew, many of whom would have been asleep on the overnight flight that departed Kuala Lumpur after midnight.